The present invention relates to a liquid crystal display element, and in one aspect relates to a twin stable-reflective liquid crystal display element that manifests a cholesteric phase at room temperature.
Various research has been conducted in recent years on reflective type liquid crystal display elements using chiral nematic liquid crystal materials, which manifest a cholesteric phase at room temperature by adding a chiral component to a nematic crystal. This type of element displays an image by switching between a planar state and a focal-conic state according to the application of high and low pulse voltages. Upon the application of a voltage, the liquid crystal material attains a homeotropic state. When the voltage is removed, the material then attains either a planar state or focal-conic state depending upon the level of voltage previously applied to the liquid crystal material. The planar and focal-conic conditions are maintained after the application of a pulse voltage (known as twin stability and memory), and the display is maintained after the voltage is removed.
Until now reflective type liquid crystal display elements have used chiral nematic liquid crystal materials, which have low reflectivity and cannot produce adequate contrast in the planar state and focal conic state, and which do not have adequate characteristics, such as color purity (excitation purity). It is important to set the drive voltage as low as possible in this type of liquid crystal element.
An object of the present invention is to provide a reflective type liquid crystal display element which has excellent twin stability and high contrast with superior characteristics such as color purity and reflectivity, and which can be set to a low drive voltage.
These objects are attained by the present invention by providing a liquid crystal display element comprising a cholesteric phase liquid crystal component and a space holding member held within a pair of substrates, wherein at least one of which is transparent. The liquid crystal component is a chiral-nematic liquid crystal material containing a liquid crystal pyrimidine compound having fluorine in the molecule, liquid crystal diphenylacetylene compound having fluorine in the molecule, and a chiral component. The liquid crystal component may also contain a liquid crystal phenylcyclohexane compound, a liquid crystal cyanobiphenyl compound, and a liquid crystal alkenyl compound.
In the present invention, characteristics such as color purity and reflectivity are improved, contrast is increased, and the drive voltage can be reduced by including in the nematic liquid crystal component a liquid crystal pyrimidine compound having fluorine within the molecule, and a liquid crystal diphenylacetylene compound containing fluorine within the molecule.